Transmitting device and method there

ABSTRACT

A transmitting device is provided. The transmitting device comprises a processor, and a transmitter; wherein the processor is configured to generate a fractional Orthogonal Frequency Division Multiplexing (OFDM) symbol based on an adjacent OFDM symbol, wherein the fractional OFDM symbol is a cyclic extension of the adjacent OFDM symbol; wherein the transmitter is configured to transmit a multicarrier signal comprising the fractional OFDM symbol and the adjacent OFDM symbol. Furthermore, the present invention also relates to a corresponding method, a multicarrier wireless communication system comprising such a transmitting device, a computer program, and a computer program product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/700,701, filed on Sep. 11, 2017, which is a continuation ofInternational Application No. PCT/EP2015/055218, filed on Mar. 12, 2015.All of the afore-mentioned patent applications are hereby incorporatedby reference in their entireties.

TECHNICAL FIELD

Embodiments of the present invention relate to a transmitting device.Furthermore, the present invention also relates to a correspondingmethod, a multicarrier wireless communication system comprising such atransmitting device, a computer program, and a computer program product.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) started a Release 13 LongTerm Evolution Advanced (LTE-Advanced) study item, Licensed AssistedAccess (LAA), aiming to use the unlicensed spectrum, on which WiFi iscurrently deployed. It is observed that LTE significantly impacts WiFiperformance in LTE-WiFi coexistence case, if current LTE functionalitiesare assumed. One major reason is that WiFi follows Listen-Before-Talk(LBT) principle, which specifies that a WiFi Node can only starttransmitting after it has performed Clear Channel Assessment (CCA) andmeasured that the channel is idle, while a legacy LTE Node does notperform CCA and may transmit continuously. The main problem for LTERelease 13 LAA is how to achieve fair and effective coexistence withWi-Fi, and among LAA networks deployed by different operators. To ensurefair co-existence with WiFi, LTE needs to be modified to also supportLBT on the unlicensed spectrum band.

To ensure fair co-existence with WiFi, it is agreed for LAA to supportLBT and discontinuous transmission as well as limited maximumtransmission duration on a carrier in the unlicensed spectrum band. TheLAA eNodeB can only start transmission when the channel is clear asmeasured by Clear Channel Assessment (CCA). After a transmission oflimited maximum duration, the LAA eNodeB needs to release the channeland perform CCA again to use the channel, resulting in opportunistictransmission with maximum transmission time of around 13 ms for LBE(Load Based Equipment) and 10 ms for Frame Based Equipment (FBE).

For LBE, CCA is minimum 20 μs, extended CCA (eCCA) duration is a randomfactor N multiplied by the CCA time, where N is randomly selected in therange 1 . . . q every time, q=4 . . . 32, and Channel Occupancy Time is<=(13/32)×q ms. For FBE, CCA is minimum 20 μs and performed in the endof IDLE period, Channel Occupancy Time is 1 ms at minimum and 10 ms atmaximum, IDLE period is Minimum 5% of channel occupancy time and FixedFrame Period=Channel Occupancy Time+IDLE Period.

For LBE, the CCA may happen at any time and the CCA success may happenat any time accordingly. One option is that at least for LBE, somesignal(s) can be transmitted by eNodeB between the time eNodeB ispermitted to transmit and the start of data transmission, at least toreserve the channel. The starting time of the signals is immediatelyafter CCA success and potentially does not fit into the OFDM symboltiming, resulting in a fractional OFDM symbol with variable length fromzero to one complete OFDM symbol.

For FBE, the DownLink (DL) transmission can only happen at the start ofthe fixed frame period. Similarly, in case the starting time of thefixed frame period is not the OFDM symbol boundary, a fractional OFDMsymbol to be transmitted.

Once the LAA eNodeB measures the channel as clear, after it transmits apotential fractional OFDM symbol to reserve the channel, it may transmita preamble for time- and frequency synchronization followed by the DLdata. The User Equipment (UE) gets synchronized to the LAA eNodeB basedon the aperiodically transmitted preamble and is able to demodulate dataimmediately after the preamble. The preamble may contain a fractionalOFDM symbol and at least one complete OFDM symbol, or may containfractional OFDM symbol only, or may contain complete OFDM symbols only.

One conventional solution is to generate the fractional OFDM symbol fromsome pre-defined sequence, e.g. random sequence, dummy sequence orZadoff-Chu (ZC) sequence. Specially, the LAA eNodeB generates the OFDMsymbol from some pre-defined sequence, e.g. random sequence, dummysequence or Zadoff-Chu (ZC) sequence, and then transmits the fractionalOFDM symbol by using a part of the OFDM symbol such that it equals theduration of the fractional OFDM symbol.

OFDM spectral efficiency is also affected by out-of-band emission, whichcreates interference by the power emission of the OFDM signal. OFDM isknown to have a rather slow decay of the spectral sidelobes, whichnecessitates the transmitter to perform one or several measures tocontrol the out-of-band emissions, e.g., transmit filtering, windowingor pulse-shaping. These methods are used to fit the spectral content ofthe signal within the limits given by spectral masks,adjacent-channel-leakage ratios and similar Out-Of-Band (OOB) emissionrequirements. Let the transmit signal on each single subcarrierrepresented by s(t), the Power Spectrum Density (PSD) of s(t) can berepresented by:

${{P\; S\;{D(f)}} = {A^{2}{T_{0}\left( \frac{\sin\left( {\pi\; f\; T_{0}} \right)}{\pi\;{fT}_{0}} \right)}^{2}}},$where A denotes the signal amplitude and T₀ is the complete symbolduration which consists of the sum of useful symbol duration T_(U) andguard interval T_(G) during which the Cyclic Prefix (CP) is transmittedto overcome Inter Symbol Interference (ISI), where the CP refers tocyclically extending the symbol. It can be observed that the PSD of anOFDM subcarrier is fulfilling a sinc function which is featured by themain lobe of the largest power is of a frequency range equal to 1/T₀,and the sidelobe is getting weaker and weaker with the frequency offsetincreasing and each sidelobe is also of a frequency range equal to 1/T₀.Therefore larger T₀ may imply the OFDM subcarrier energy is moreconcentrated in its allocated frequency and less power emission.

If the modulation symbols on the different subcarriers are uncorrelated,the PSD of the OFDM signal comprising N subcarriers can be expressed as:

${P\; S\;{D(f)}} = {\sum\limits_{k = 0}^{N - 1}{A^{2}{{T_{0}\left( \frac{\sin\left( {{\pi\left( {f - f_{k}} \right)}T_{0}} \right)}{{\pi\left( {f - f_{k}} \right)}T_{0}} \right)}^{2}.}}}$As the symbol duration of the fractional OFDM symbol T_(0_F) is shorterthan the normal complete OFDM symbol duration T₀, the power emission maybe increased where it is assumed that the bandwidth is 20 MHz, theeNodeB transmission power is 36 dBm, the FFT size is 2048, and the CPlength is 144/(15000*2048) second. It can be observed that the poweremission is increased if the fractional OFDM symbol duration is of ¾useful symbol duration (¾ T_(U)), and is further increased if thefraction OFDM symbol is reduced to ½ useful symbol duration (½ T_(U)),or to ¼ useful symbol duration (¼ T_(U)).

The increased out-of-band emissions due to fractional OFDM symbols willreduce the performance of the wireless communication system. It is alsonon-trivial to provide means in the transmitter for controlling thespectral emissions. In a typical OFDM system, the OFDM symbols have thesame (or very similar) duration. Therefore, the transmitter canimplement a transmit filter based on a typical OFDM symbol duration.Such filters are typically implemented in hardware as the filtercoefficients may not to be changed dynamically. However, with fractionalOFDM symbols, which may have varying length depending on the CCAprocess, the transmit filter design would be more complicated, allowingdynamic duration OFDM symbols, which will increase the cost of thefilter.

In addition, during the fractional OFDM symbol period, there would beother communication devices performing CCA measurements on the adjacentbands, e.g. LAA or WiFi devices. If there is an increase of OOB emissiondue to reduced symbol duration, this may introduce more severeinterference to other LAA Nodes, resulting in a smaller probability of asuccessfully reserving the channel, further resulting in unnecessaryblocking of the transmissions on the adjacent bands.

One disadvantage of conventional solutions is the additional complexitydue to generation of OFDM symbol from some pre-defined sequence, e.g.random sequence, dummy sequence or Zadoff-Chu (ZC) sequence. This mayeither result in FFT processing and OFDM modulation process for eachfractional OFDM symbol transmission, or additional resource to store thepre-generated OFDM symbols samples.

A further disadvantage of conventional solutions is that it is notpossible to generate arbitrarily short OFDM symbols. For example, in theLTE eNodeB, there could be a transient period of 17 microseconds whenchanging from an OFF state (i.e., no transmit power) to an ON state(i.e., full transmit power).

Another disadvantage of conventional solutions is increased OOB emissiondue to reduced symbol duration of a fractional OFDM symbol.

SUMMARY

An objective of embodiments of the present invention is to provide asolution which mitigates or solves the drawbacks and problems ofconventional solutions.

Another objective of embodiments of the present invention is to providefractional OFDM signals which are able to reserve the channel while alsosupporting low-complex implementations of the fractional OFDM signalgeneration as well as reducing out-of-band emissions.

An “or” in this description and the corresponding claims is to beunderstood as a mathematical OR which covers “and” and “or”, and is notto be understand as an XOR (exclusive OR).

The above objectives are solved by the subject matter of the independentclaims. Further advantageous implementation forms of the presentinvention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned andother objectives are achieved with a transmitting device for amulticarrier wireless communication system, the transmitting devicecomprising:

a processor, and

a transmitter;

wherein the processor is configured to generate a fractional OrthogonalFrequency Division Multiplexing, OFDM, symbol based on an adjacent OFDMsymbol, wherein the fractional OFDM symbol is a cyclic extension of theadjacent OFDM symbol;

wherein the transmitter is configured to transmit a multicarrier signalcomprising the fractional OFDM symbol and the adjacent OFDM symbol.

With a transmitting device configured to transmit a multicarrier signalcomprising the present fractional OFDM symbol and at least one adjacentOFDM symbol a number of advantages are provided.

An advantage is reduced implementation complexity for generating thefractional OFDM symbol due to simple re-use, or small changes, of themethod used for generating the adjacent OFDM symbol.

Another advantage is reduced out-of-band power emission due to longersymbol duration.

Yet another advantage is reduced implementation complexity of thetransmit filters.

Yet another advantage is larger tolerance for inter-symbol-interferencefor the adjacent OFDM symbol.

Yet another advantage is that the duration of the fractional OFDM symbolis not constrained by the OFF-to-ON transient time in the transmitter.

In a first possible implementation form of a transmitting deviceaccording to the first aspect, by cyclically extending the adjacent OFDMsymbol, the multicarrier signal is continuous at the boundary betweenthe fractional OFDM symbol and the adjacent OFDM symbol.

With the first possible implementation form the above stated advantagesfor the first aspect are applicable.

In a second possible implementation form of a transmitting deviceaccording to the first possible implementation form of the first aspect,by cyclically extending the adjacent OFDM symbol, each subcarrierwaveform of the multicarrier signal is continuous at the boundarybetween the fractional OFDM symbol and the adjacent OFDM symbol.

With the second possible implementation form the above stated advantagesfor the first aspect are applicable.

In a third possible implementation form of a transmitting deviceaccording to the second possible implementation form of the firstaspect, by cyclically extending the adjacent OFDM symbol, the modulationsymbol of a subcarrier in the fractional OFDM symbol is the samemodulation symbol as the modulation symbol of the correspondingsubcarrier in the adjacent OFDM symbol.

With the third possible implementation form the above stated advantagesfor the first aspect are applicable.

In a fourth possible implementation form of a transmitting deviceaccording to any of the preceding possible implementation forms of thefirst aspect or to the first aspect as such, wherein the symbol durationof the fractional OFDM symbol is shorter than the symbol duration of theadjacent OFDM symbol.

With the fourth possible implementation form the above stated advantagesfor the first aspect are applicable.

In a fifth possible implementation form of a transmitting deviceaccording to any of the preceding possible implementation forms of thefirst aspect or to the first aspect as such, the adjacent OFDM symbolcomprises one cyclic prefix.

With the fifth possible implementation form the above stated advantagesfor the first aspect are applicable.

In a sixth possible implementation form of a transmitting deviceaccording to any of the preceding possible implementation forms of thefirst aspect or to the first aspect as such, the fractional OFDM symbolis immediately followed or immediately preceded by the adjacent OFDMsymbol.

With the sixth possible implementation form the above stated advantagesfor the first aspect are applicable.

In a seventh possible implementation form of a transmitting deviceaccording to any of the preceding possible implementation forms of thefirst aspect or to the first aspect as such, the fractional OFDM symbolis transmitted before an OFDM symbol used for data channels or controlchannels.

With the seventh possible implementation form the above statedadvantages for the first aspect are applicable.

In an eighth possible implementation form of a transmitting deviceaccording to any of the preceding possible implementation forms of thefirst aspect or to the first aspect as such, the multicarrier signal istransmitted in unlicensed spectrum of the multicarrier wirelesscommunication system.

With the eighth possible implementation form the above stated advantagesfor the first aspect are applicable.

The present invention also relates to a multicarrier wirelesscommunication system comprising at least one transmitting deviceaccording to any of the preceding possible implementation forms of thefirst aspect or to the first aspect as such.

According to a second aspect of the invention, the above mentioned andother objectives are achieved with a method for a multicarrier wirelesscommunication system, the method comprising:

generating a fractional Orthogonal Frequency Division Multiplexing(OFDM) symbol based on an adjacent OFDM symbol, wherein the fractionalOFDM symbol is a cyclic extension of the adjacent OFDM symbol; and

transmitting a multicarrier signal comprising the fractional OFDM symboland the adjacent OFDM symbol.

In a first possible implementation form of a method according to thesecond aspect, by cyclically extending the adjacent OFDM symbol, themulticarrier signal is continuous at the boundary between the fractionalOFDM symbol and the adjacent OFDM symbol.

In a second possible implementation form of a method according to thefirst possible implementation form of the second aspect, by cyclicallyextending the adjacent OFDM symbol, each subcarrier waveform of themulticarrier signal is continuous at the boundary between the fractionalOFDM symbol and the adjacent OFDM symbol.

In a third possible implementation form of a method according to thesecond possible implementation form of the second aspect, by cyclicallyextending the adjacent OFDM symbol, the modulation symbol of asubcarrier in the fractional OFDM symbol is the same modulation symbolas the modulation symbol of the corresponding subcarrier in the adjacentOFDM symbol.

In a fourth possible implementation form of a method according to any ofthe preceding possible implementation forms of the second aspect or tothe second aspect as such, wherein the symbol duration of the fractionalOFDM symbol is shorter than the symbol duration of the adjacent OFDMsymbol.

In a fifth possible implementation form of a method according to any ofthe preceding possible implementation forms of the second aspect or tothe second aspect as such, the adjacent OFDM symbol comprises one cyclicprefix.

In a sixth possible implementation form of a method according to any ofthe preceding possible implementation forms of the second aspect or tothe second aspect as such, the fractional OFDM symbol is immediatelyfollowed or immediately preceded by the adjacent OFDM symbol.

In a seventh possible implementation form of a method according to anyof the preceding possible implementation forms of the second aspect orto the second aspect as such, the fractional OFDM symbol is transmittedbefore an OFDM symbol used for data channels or control channels.

In an eighth possible implementation form of a method according to anyof the preceding possible implementation forms of the second aspect orto the second aspect as such, the multicarrier signal is transmitted inunlicensed spectrum of the multicarrier wireless communication system.

The advantages of the methods according to the second aspect are thesame as those for the corresponding transmitting device according to thefirst aspect.

The present invention also relates to a computer program with a programcode, which when runs by processing means causes said processing meansto execute any method according to the present invention. Further, theinvention also relates to a computer program product comprising acomputer readable medium and said mentioned computer program, whereinsaid computer program is included in the computer readable medium, andcomprises of one or more from the group: ROM (Read-Only Memory), PROM(Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM(Electrically EPROM) and hard disk drive.

Further applications and advantages of the present invention will beapparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are intended to clarify and explain differentembodiments of the present invention, in which:

FIG. 1 shows a transmitting device according to an embodiment of thepresent invention;

FIG. 2 shows a method according to an embodiment of the presentinvention;

FIG. 3 shows the PSD for OFDM symbols of different duration showing thatthe OOB emissions decrease for fractional OFDM symbols being generatedas cyclic extensions of a subsequent OFDM symbol;

FIG. 4 illustrates the generation of the fractional OFDM symbol in a waythat the fractional OFDM symbol is a cyclic extension of the subsequentOFDM symbol;

FIG. 5 illustrates the generation of the fractional OFDM symbol in a waythat the fractional OFDM symbol is a cyclic extension of the subsequentOFDM symbol;

FIG. 6 illustrates the generation of the fractional OFDM symbol in a waythat the fractional OFDM symbol is a cyclic extension of the previousOFDM symbol; and

FIG. 7 illustrates a multicarrier wireless communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a transmitting device 100 according to an embodiment of thepresent invention. The transmitting device 100 comprises a processor 102and a transmitter 104 (e.g. part of a transceiver device). The processor102 is communicably coupled with the transmitter 104 with communicationmeans (illustrated with the dashed arrow) known in the art. Thetransmitter 104 is further coupled to an antenna device 106 configuredfor wireless communications in the multicarrier wireless communicationsystem 500 which is illustrated with dashed lines in FIG. 1. Thewireless communications may be according to suitable communicationstandards, such as e.g. 3GPP standards.

The processor 102 of the transmitting device 100 is configured togenerate a fractional OFDM signal based on an adjacent OFDM symbol, suchthat the fractional OFDM symbol is a cyclic extension of the adjacentOFDM symbol. Hence, the fractional OFDM symbol is immediately followedor immediately preceded by the adjacent OFDM symbol according to anembodiment of the present invention. The generated fractional OFDMsymbol is forwarded to the transmitter 104 after being generated. Thetransmitter 104 is configured to receive the fractional OFDM symbol fromthe processor 102 and further configured to transmit a multicarriersignal S_(MC) comprising the fractional OFDM symbol and the adjacentOFDM symbol in the multicarrier wireless communication system 500. Themulticarrier signal S_(MC) is in the example in FIG. 1 transmitted viathe antenna device 106 of the transmitting device 100.

The transmitting device 100 can be any suitable communication devicehaving the capabilities and being configured to transmit multicarriersignals in a wireless communication system 500. It should is noted thatthe transmitting device 100 also comprises other means, units, elements,devices, etc., such that the transmitting device 100 has the mentionedcapabilities. Examples of such means, units, elements, and devices aregiven in the following description. Further, examples of suchcommunication devices are radio network nodes and user devices.

A radio network node, such as a base station, e.g. a Radio Base Station(RBS), which in some networks may be referred to as transmitter, “eNB”,“eNodeB”, “NodeB” or “B node”, depending on the technology andterminology used. The radio network nodes may be of different classessuch as e.g. macro eNodeB, home eNodeB or pico base station, based ontransmission power and thereby also cell size. The radio network nodecan be a station (STA), which is any device that contains an IEEE802.11-conformant media access control (MAC) and physical layer (PHY)interface to the wireless medium (WM).

A user device, such as a User Equipment (UE), mobile station, wirelessterminal and/or mobile terminal is enabled to communicate wirelessly ina wireless communication system, sometimes also referred to as acellular radio system. The UE may further be referred to as mobiletelephones, cellular telephones, computer tablets or laptops withwireless capability. The UEs in the present context may be, for example,portable, pocket-storable, hand-held, computer-comprised, orvehicle-mounted mobile devices, enabled to communicate voice and/ordata, via the radio access network, with another entity, such as anotherreceiver or a server. The UE can be a station (STA), which is any devicethat contains an IEEE 802.11-conformant media access control (MAC) andphysical layer (PHY) interface to the wireless medium (WM).

The disclosed solution is applicable to all coded modulationtransmission systems sending information to multiple users, possiblycombined with OFDM and Multiple Input Multiple Output (MIMO)transmissions. For example, 3GPP LAA systems can take advantage of thepresent solution. Therefore, according to an embodiment of the presentinvention the multicarrier signal S_(MC) is transmitted in unlicensedspectrum of the multicarrier wireless communication system 500.

FIG. 2 shows a general flow chart of a method 200 according to anembodiment of the present invention. The method 200 may be executed in atransmitting device 200, such as the one shown in FIG. 1. The method 200comprises the first step of generating 202 a fractional OFDM symbolbased on an adjacent OFDM symbol. The fractional OFDM symbol is, asdescribed above, a cyclic extension of the adjacent OFDM symbol. Themethod 200 further comprises the second step of transmitting 204 amulticarrier signal S_(MC) comprising the fractional OFDM symbol and theadjacent OFDM symbol.

The generated fractional OFDM symbol has no fixed duration and may beadjacent with an OFDM symbol containing preamble, or an OFDM symbolcontaining data and/or control information according to embodiments ofthe present invention.

The length of the fractional OFDM symbol is not fixed and may change foreach time the transmitting device 100 (such as a LAA eNodeB) transmitsthe multicarrier signal S_(MC). This is because the transmitting device100 may start transmission once it measures the channel as clear and itcan be at any time during a subframe.

Embodiments of the present invention disclose to generate the fractionalOFDM symbol from the adjacent OFDM symbol in a way comprising at leastone of the following: the fractional OFDM symbol is a cyclic extensionof the subsequent OFDM symbol; or the fractional OFDM symbol is a cyclicextension of the previous OFDM symbol.

A cyclic extension implies that the signal is continuous between thefractional OFDM symbol and the subsequent/previous OFDM symbol. One wayof cyclic extension is to assure that each subcarrier waveform iscontinuous between the fractional OFDM symbol and thesubsequent/previous OFDM symbol, which can be achieved by, for eachsubcarrier, use the same modulation symbol in the fractional OFDM symboland the subsequent/previous OFDM symbol.

Therefore, embodiments of the present invention consider two consecutiveOFDM symbols, i.e. the fractional OFDM symbol and the adjacent OFDMsymbol. The adjacent OFDM symbol could be an OFDM symbol containingpreamble, or an OFDM symbol containing data and/or control information.

The adjacent OFDM symbol could comprise a cyclic prefix. Moreover,typically an OFDM symbol has a duration of its useful part, T_(U), suchthat each subcarrier produces an integer number of periods during T_(U),where the number of periods depend on the subcarrier frequency.Embodiments of the present invention is applicable to where the durationof the useful part of the adjacent OFDM symbol is such that eachsubcarrier produces an integer number of periods during the usefulperiod. A skilled person in the art will also be able to apply thepresent solution by performing a cyclic extension for cases where theduration of the useful part of the adjacent OFDM symbol is such thateach subcarrier does not produce an integer number of periods during theuseful period.

In the following description LTE terminology and systems are consideredfor exemplifying embodiments of the present invention. It should howeverbe noted that the present solutions is not limited hereto.

In the LTE system, the time-continuous signal s_(l) ^((p))(t) on antennaport p in OFDM symbol l in a downlink slot is defined by

${s_{l}^{(p)}(t)} = {{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}}}$for 0≤t<(N_(CP,l)+N)×T_(s) where k⁽⁻⁾=k+└N_(RB) ^(DL)N_(sc) ^(RB)/2┘ andk⁽⁺⁾=k+└N_(RB) ^(DL)N_(sc) ^(RB)/2┘−1, resource element (k,l) on antennaport p corresponds to the complex value a_(k,l) ^((p)), T=1/(15000*2048)second N_(sc) ^(RB)=12 and N_(RB) ^(DL) is related to the systembandwidth, e.g. it assumes the value 100 for 20 MHz bandwidth.

The variable N equals 2048 for Δf=15 kHz subcarrier spacing and 4096 forΔf=7.5 kHz subcarrier spacing. The OFDM symbols in a slot shall betransmitted in increasing order of l, starting with l=0, where OFDMsymbol l>0 starts at time Σ_(l′=0) ^(l-1)(N_(CP,l′)+N)T_(s) within theslot. The value of N_(CP,l) is given in Table 1 below for LTE.

TABLE 1 OFDM signal parameters in LTE Configuration Cyclic prefix lengthN_(CP, l) Normal cyclic prefix Δf = 15 kHz 160 for l = 0 144 for l = 1,2, . . . , 6 Extended cyclic prefix Δf = 15 kHz 512 for l = 0, 1, . . ., 5 Δf = 7.5 kHz 1024 for l = 0, 1, 2

In embodiments of the present invention, the fractional OFDM symbol l′followed by the OFDM symbol l can be generated as

${s_{l^{\prime}}^{(p)}(t)} = {{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}} - T_{0{\_ F}}})}}}}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}} - T_{0{\_ F}}})}}}}}}$for 0≤t≤T_(0_F). It can be observed each subcarrier waveform iscontinuous between the fractional OFDM symbol l′ and the subsequent OFDMsymbol l because

${{\lim\limits_{t\rightarrow T_{0{\_ F}}}{s_{k,l^{\prime}}^{(p)}(t)}} = {{a_{k,l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}} = {s_{k,l}^{(p)}(0)}}},$where k is the subcarrier index.

In addition, the signal between the fractional OFDM symbol l′ and thesubsequent OFDM symbol l is also continuous because

${\lim\limits_{t\rightarrow T_{0{\_ F}}}{s_{l^{\prime}}^{(p)}(t)}} = {{{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({{- N_{{CP},l}}T_{s}})}}}}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({{- N_{{CP},l}}T_{s}})}}}}}} = {s_{l}^{(p)}(0)}}$

In this way the fractional OFDM symbol l′ is a cyclic extension of thesubsequent OFDM symbol, where the following condition is fulfilleds _(l′) ^((p))(t)=s _(l) ^((p))(NT _(s) −T _(0_F) +t).

Without loss of generality, the cyclic extension of the subsequent OFDMsymbol can also be expressed byF ^(p)(t)=S ^((p))(T _(u) −T _(0_F) +t) or F ^(p)(t)=S ^((p))((T _(u) −T_(0_F) +t)mod(T _(u) +T _(G))),where F^((p))(t) is the fractional OFDM symbol on antenna port p in thetime domain with symbol duration T_(0_F); mod is modulo operation; andS^((p))(t) is the subsequent OFDM symbol on antenna port p with apositive information symbol duration T_(u) and a non-negative cyclicprefix duration T_(CP).

By generating the fractional OFDM symbol as a cyclic extension of thesubsequent OFDM symbol, the OFDM symbol duration is prolonged comparedwith the concerned fractional OFDM symbol, and also the subsequent OFDMsymbol, resulting in reduced power emission, as shown in FIG. 3 wherethe x-axis shows the frequency offset and the y-axis shows the PSD.

In one other embodiment of the present invention, the fractional OFDMsymbol is generated from the previous OFDM symbol. The fractional OFDMsymbol l′ following the OFDM symbol l can be generated as:

${s_{l^{\prime}}^{(p)}(t)} = {{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{ft}}}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{ft}}}}}$for 0≤t<T_(0_F). It can be observed each subcarrier waveform iscontinuous between the fractional OFDM symbol l′ and the previous OFDMsymbol l because

${{s_{k,l^{\prime}}^{(p)}(0)} = {a_{k,l}^{(p)} = {\lim\limits_{t\rightarrow{{({N_{{CP},l} + N})} \times T_{s}}}{s_{k,l}^{(p)}(t)}}}},$where k is the subcarrier index.

In addition, the signal between the fractional OFDM symbol l′ and theprevious OFDM symbol l is also continuous because

${\lim\limits_{t\rightarrow{{({N_{{CP},l} + N})} \times T_{s}}}{s_{l}^{(p)}(t)}} = {{{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}a_{k^{( - )},l}^{(p)}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}a_{k^{( + )},l}^{(p)}}} = {{s_{l^{\prime}}^{(p)}(0)}.}}$

In this way the fractional OFDM symbol l′ is a cyclic extension of theprevious OFDM symbol, where the subcarrier spacing concerning thefractional OFDM symbol is the same as the subcarrier spacing concerningthe previous OFDM symbol l, and the following condition is fulfilleds _(l′) ^((p))(t)=s _(l) ^((p))(N _(CP,l) T _(s) +t).

Without loss of generality, the cyclic extension of the previous OFDMsymbol can also be expressed byF ^(p)(t)=S ^((p))((T _(CP) +t)mod(T _(u) +T _(CP))),where F^(p)(t) is the fractional OFDM symbol on antenna port p in thetime domain; mod is the modulo operation; and S^((p))(t) is the previousOFDM symbol on antenna port p with a positive information symbolduration T_(u) and a non-negative cyclic prefix duration T_(CP).

In another example of the present invention, the adjacent OFDM symbol isan OFDM symbol with at least one subcarrier not having an integer numberof periods. The time-continuous signal s_(l) ^((p))(t) on antenna port pin the adjacent OFDM symbol l in a downlink slot is defined by

${s_{l}^{(p)}(t)} = {{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\;\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}}}$for T_(start)≤t<T_(end), where T_(end)−T_(start)<NT_(s). Subcarrier khas a period of 1/(kΔf) and since NT_(s)=1/Δf, then there is an integernumber of periods within the duration of NT_(s). Therefore ifT_(end)−T_(start)<NT_(s) then there is at least one subcarrier nothaving an integer number of periods.

In one embodiment of the present invention, the fractional OFDM symbolis generated from the following/subsequent OFDM symbol in a way that thefractional OFDM symbol is the cyclic extension of the subsequent OFDMsymbol. One example assuming the subsequent OFDM symbol is an OFDMsymbol containing CP and useful OFDM symbol is illustrated in FIG. 4. Itshould be noted that the x-axis in FIGS. 4-6 represent time T.

As shown in FIG. 4 the fractional OFDM symbol with duration T_(0_F) is acyclic extension of the subsequent OFDM symbol. The subsequent OFDMsymbol is in this particular example an OFDM symbol comprising CP withduration T_(G) and useful information with duration T_(U).

In another embodiment of the present invention, the subsequent OFDMsymbol is an OFDM symbol without CP as illustrated in FIG. 5. This maybe used for many purposes, e.g. for purpose of reducing the overhead. InFIG. 5 the fractional OFDM symbol with duration T_(0_F) is a cyclicextension of the subsequent OFDM symbol without CP. Generating thefractional OFDM symbol as a cyclic extension of the subsequent OFDMsymbol still provides the advantages of simple implementation andprolonged symbol duration to reduce out-of-band power emissions.

In a further embodiment of the present invention, the fractional OFDMsymbol is generated from the subsequent OFDM symbol in a way that themulticarrier signal S_(MC) is continuous at the boundary between thefractional OFDM symbol and the subsequent OFDM symbol. One example ofgenerating continuous symbols is by means of N-continuous OFDM.

In further embodiments of the present invention, the fractional OFDMsymbol is generated from the previous OFDM symbol in a way that thefractional OFDM symbol is a cyclic extension of the previous OFDMsymbol.

In one example the fractional OFDM symbol with duration T_(0_F) startsnot at the OFDM symbol boundary and could be used to at least reservethe channel until the downlink transmission carrying other usefulinformation happens, e.g. downlink transmission for control informationor data. The fractional OFDM symbol starts immediately after theprevious OFDM symbol and ends at the OFDM subframe boundary. In thiscase the fractional OFDM symbol is a cyclic extension of the previousOFDM symbol. The previous OFDM symbol may start immediately when thetransmitting device 100 measures the channel as clear.

In a further embodiment of the present invention, the fractional OFDMsymbol is generated from the subsequent/previous OFDM symbol by means ofmanipulation of the subsequent/previous OFDM symbol. The manipulationincludes but is not limited to manipulations, such as multiplication ofthe subsequent OFDM symbol by a real or complex value, the shifts orcyclic shifts of the subsequent OFDM symbol, truncation, puncturing,using different parameters defining the subsequent OFDM symbol (e.g.,root indices, initialization values of shift registers, etc.), otherlinear transformations and any other means using the subsequent OFDMsymbol.

FIG. 7 illustrates a multicarrier wireless communication system 500according to an embodiment of the present invention. The transmittingdevice 100 is in this example a LAA eNodeB configured to transmitdownlink signals in a cellular multicarrier communication system. InFIG. 7 also two exemplary User Devices (UDs) UD1 and UD2 are shown. TheUDs may be any mobile station or corresponding devices known in the art,such as UEs. The transmitting device 100 transmits one or moremulticarrier signals S_(MC) in the downlink. UD1 and UD2 are configuredto receive the multicarrier signal(s) S_(MC) from the transmittingdevice 100. UD1 and UD2 get synchronized to the LAA eNodeB based on theaperiodically transmitted preamble and are able to demodulate dataimmediately after the preamble. The preamble may contain a fractionalOFDM symbol and at least one complete OFDM symbol, or may containfractional OFDM symbol only, or may contain complete OFDM symbols only.

Furthermore, any method according to the present invention may beimplemented in a computer program, having a program code, which whenruns by processing means causes the processing means to execute thesteps of the method. The computer program is included in a computerreadable medium of a computer program product. The computer readablemedium may comprises of essentially any memory, such as a ROM (Read-OnlyMemory), a PROM (Programmable Read-Only Memory), an EPROM (ErasablePROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a harddisk drive.

Moreover, it is realized by the skilled person that the presenttransmitting device 100 comprises the necessary communicationcapabilities in the form of e.g., functions, means, units, elements,etc., for performing the present solution. Examples of other such means,units, elements and functions are: processors, memory, buffers, controllogic, encoders, decoders, rate matchers, de-rate matchers, mappingunits, multipliers, decision units, selecting units, switches,interleavers, de-interleavers, modulators, demodulators, inputs,outputs, antennas, amplifiers, receiver units, transmitter units, DSPs,MSDs, TCM encoder, TCM decoder, power supply units, power feeders,communication interfaces, communication protocols, etc. which aresuitably arranged together for performing the present solution.

Especially, the processors of the present devices may comprise, e.g.,one or more instances of a Central Processing Unit (CPU), a processingunit, a processing circuit, a processor, processing mean, an ApplicationSpecific Integrated Circuit (ASIC), a microprocessor, or otherprocessing logic that may interpret and execute instructions. Theexpression “processor” may thus represent a processing circuitrycomprising a plurality of processing circuits, such as, e.g., any, someor all of the ones mentioned above. The processing circuitry may furtherperform data processing functions for inputting, outputting, andprocessing of data comprising data buffering and device controlfunctions, such as call processing control, user interface control, orthe like.

Finally, it should be understood that the present invention is notlimited to the embodiments described above, but also relates to andincorporates all embodiments within the scope of the appendedindependent claims.

The invention claimed is:
 1. A transmitting device for a wirelesscommunication system, the transmitting device comprising: a processorconfigured to generate a fractional orthogonal frequency divisionmultiplexing (OFDM) symbol based on an adjacent OFDM symbol, wherein thefractional OFDM symbol is a cyclic extension of the adjacent OFDM symbolsuch that a modulation symbol of a subcarrier in the fractional OFDMsymbol is the same modulation symbol as a modulation symbol of asubcarrier in the adjacent OFDM symbol associated with the subcarrier inthe fractional OFDM symbol; and a transmitter configured to cooperatewith the processor to transmit a signal comprising the fractional OFDMsymbol and the adjacent OFDM symbol once the transmitter device measuresthe channel as clear.
 2. The transmitting device according to claim 1,wherein, by cyclically extending the adjacent OFDM symbol, the signal iscontinuous at the boundary between the fractional OFDM symbol and theadjacent OFDM symbol.
 3. The transmitting device according to claim 2,wherein, by cyclically extending the adjacent OFDM symbol, eachsubcarrier waveform of the signal is continuous at the boundary betweenthe fractional OFDM symbol and the adjacent OFDM symbol.
 4. Thetransmitting device according to claim 1, wherein a symbol duration ofthe fractional OFDM symbol is shorter than a symbol duration of theadjacent OFDM symbol.
 5. The transmitting device according to claim 1,wherein the adjacent OFDM symbol comprises one cyclic prefix.
 6. Thetransmitting device according to claim 1, wherein the fractional OFDMsymbol is immediately followed or immediately preceded by the adjacentOFDM symbol.
 7. The transmitting device according to claim 1, whereinthe transmitter is configured to cooperate with the processor totransmit the fractional OFDM symbol before an OFDM symbol which is usedfor data channels or control channels.
 8. The transmitting deviceaccording to claim 1, wherein the transmitter is configured to cooperatewith the processor to transmit the signal in an unlicensed spectrum ofthe wireless communication system.
 9. A method for a wirelesscommunication system, the method comprising: generating, by atransmitting device, a fractional orthogonal frequency divisionmultiplexing (OFDM) symbol based on an adjacent OFDM symbol, wherein thefractional OFDM symbol is a cyclic extension of the adjacent OFDM symbolsuch that a modulation symbol of a subcarrier in the fractional OFDMsymbol is the same modulation symbol as a modulation symbol of asubcarrier in the adjacent OFDM symbol associated with the subcarrier inthe fractional OFDM symbol; and transmitting, by the transmittingdevice, a signal comprising the fractional OFDM symbol and the adjacentOFDM symbol once the transmitting device measures the channel as clear.10. The method according to claim 9, wherein, by cyclically extendingthe adjacent OFDM symbol, the signal is continuous at the boundarybetween the fractional OFDM symbol and the adjacent OFDM symbol.
 11. Themethod according to claim 10, wherein, by cyclically extending theadjacent OFDM symbol, each subcarrier waveform of the signal iscontinuous at the boundary between the fractional OFDM symbol and theadjacent OFDM symbol.
 12. The method according to claim 9, wherein asymbol duration of the fractional OFDM symbol is shorter than a symbolduration of the adjacent OFDM symbol.
 13. The method according to claim9, wherein the adjacent OFDM symbol comprises one cyclic prefix.
 14. Themethod according to claim 9, wherein the fractional OFDM symbol isimmediately followed or immediately preceded by the adjacent OFDMsymbol.
 15. The method according to claim 9, wherein the fractional OFDMsymbol is transmitted before an OFDM symbol which is used for datachannels or control channels.
 16. The method according to claim 9,wherein the signal is transmitted in an unlicensed spectrum of thewireless communication system.
 17. A non-transitory computer-readablememory having processor-executable instructions stored thereon for awireless communication system, the processor-executable instructions,when executed, facilitating performance of the following: generating afractional orthogonal frequency division multiplexing (OFDM) symbolbased on an adjacent OFDM symbol, wherein the fractional OFDM symbol isa cyclic extension of the adjacent OFDM symbol such that a modulationsymbol of a subcarrier in the fractional OFDM symbol is the samemodulation symbol as a modulation symbol of a subcarrier in the adjacentOFDM symbol associated with the subcarrier in the fractional OFDMsymbol; and transmitting a signal comprising the fractional OFDM symboland the adjacent OFDM symbol once the channel is measured as clear. 18.The non-transitory computer-readable memory method according to claim17, wherein a symbol duration of the fractional OFDM symbol is shorterthan a symbol duration of the adjacent OFDM symbol.
 19. Thenon-transitory computer-readable memory according to claim 17, whereinthe adjacent OFDM symbol comprises one cyclic prefix.
 20. Thenon-transitory computer-readable memory according to claim 17, whereinthe fractional OFDM symbol is immediately followed or immediatelypreceded by the adjacent OFDM symbol.
 21. The non-transitorycomputer-readable memory according to claim 17, wherein the fractionalOFDM symbol is transmitted before an OFDM symbol which is used for datachannels or control channels.
 22. The non-transitory computer-readablememory according to claim 17, wherein the signal is transmitted in anunlicensed spectrum of the wireless communication system.